Hard ceramic materials such as oxides, carbides, nitrides and borides are engineered materials having high melting or decomposition temperature, high hardness, strength and wear resistance and resistance to high temperature oxidation and degradation as well as resistance to corrosive chemicals such as acids and bases. These ceramic materials have found applications in tools, dies, grinding media, heating elements, furnace insulations, thermal shields, high temperature probe sheathing, and variety of other demanding applications. In particular, the group of compounds known as metal borides are exceptionally hard and chemically inert and are very attractive candidates for high technology applications which require high performance as indicated above. Some known borides are titanium diboride (TiB2), iron boride (FeB), chromium boride (CrB), molybdenum boride (MoB), tantalum boride (TaB), zirconium boride (ZrB2) and hafnium boride (HfB2). Of these, only titanium diboride is widely manufactured commercially due to its high melting temperature, hardness and wear resistance as well as electrical conductivity. Other borides are not widely available due to difficulties in making pure and dense materials, as well as attendant high manufacturing costs.
Commercially, titanium diboride is first manufactured as a powder by reacting titanium oxide with boron. The pure titanium diboride powder is then consolidated by hot pressing above 2200° C. under pressure of several thousand Pascals to produce bulk and solid material. The higher temperatures and pressures involved make this material quite expensive. Hence, use of this material has been limited to specialized and value-added markets. Although the high hardness (3200 Kg/mm2 Vickers hardness) is attractive, hardness exceeding 2000 Kg/mm2 is seldom required in common applications. Additionally, the high cost of making titanium diboride, as well as difficulties in obtaining fully densified titanium diboride limits its flexural strength to about 300 MPa and its use to applications where there is no viable alternative.
There have been efforts focused on providing titanium alloys reinforced with titanium monoboride whiskers and such materials which have improved hardness and wear resistance characteristics relative to titanium. For example, a number of researchers have formed titanium metal having titanium monoboride needles distributed throughout the titanium matrix. Further, some attempts have been made to produce materials having a high content of titanium monoboride. However, typically, such materials also have substantial amounts of residual titanium metal and titanium diboride which significantly reduces the strength of the titanium monoboride material.
Silicon nitride is among the strongest materials for similar wear resistant applications and can have strength of about 700 MPa. Further, it has a hardness of about 1800 Kg/mm2. However, silicon nitride is not electrically conductive, which means making of complex shapes and profiles is to be done by diamond-based machining which is complicated and expensive. Further, titanium diboride which is another common material for use in wear resistant applications, requires process temperatures above 2200° C. in order to form the material. Achieving full density is cumbersome, requiring even higher temperatures, pressures, and process times. Additional problems are more coarse grains and non-uniform grain structure which are some of the causes of relatively low strength (<300 MPa) titanium diboride. The high temperatures and pressures required significantly increase the costs of manufacture.
For this and other reasons, the need remains for methods and materials which can provide new or improved materials for use where extremely high strength alloys are required, which have decreased manufacturing costs and avoid the drawbacks mentioned above.